Venous thromboembolism (VTE) is a spectrum of disease involving clot formation in the deep limb veins or in the lungs. This disease is the most common cause of death at 30 days after cancer surgery, with a large proportion of these events occurring after hospital discharge. With over 400,000 cancer-associated venous thromboembolic events annually in the United States, the annual cost is estimated to be over $8 billion a year. VTE can be prevented by prophylactic medications, but there are no clear guidelines to help clinicians know which patients should receive these medications when they leave the hospital. To date, there have been no clinical trials aimed at developing a prognostic risk score to identify cancer surgery patients at high risk of VTE. If such a score can be developed, morbidity and mortality after cancer surgery could be reduced. Newer laboratory tests of hypercoagulable state have potential value in identifying high risk patients and should be included in any prognostic model. The thromboelastogram (TEG) is a laboratory test of hypercoagulable state that has excellent predictive value on inpatients for VTE, and should be tested in surgical oncology after discharge. We propose to conduct a prospective observational study to develop a prognostic risk score to identify surgical oncology patients at high risk of VTE after hospital discharge. Both clinical and laboratory parameters will be included in the model. We plan to enroll 300 gastrointestinal and urological cancer surgery patients over the course of 4 years. The TEG and other laboratory tests will be performed at hospital discharge. VTE will be assessed at 3 months. Logistic regression will be used build a prognostic model for post-discharge VTE. The prognostic score developed in this study will be used to identify a suitably high-risk population of patients for enrollment in a subsequent multi-center trial of postdischarge VTE prophylaxis in surgical oncology patients. Specific Aim #1: Construct a prognostic model of postdischarge VTE in surgical oncology patients, incorporating clinical and laboratory variables. Specific Aim #2: Calculate the predictive accuracy of the TEG in predicting VTE. Specific Aim #3: Characterize the postoperative coagulation status of surgical oncology patients with regards to specific elements of the coagulation cascade. This has important implications for rationale selection of prophylactic medications in these patients.